Magnetic refrigeration is a promising technology capable of achieving sub-Kelvin temperatures without using 3 He. However, conventional magnetocaloric materials suffer from drawbacks such as high driving magnetic fields, low magnetic entropy change (Δ S M ), and structural instability, limiting their practical application. In this work, KGdF 4 with different crystal structures was synthesized, and the structure dependence of the magnetocaloric effect (MCE) was investigated. Notably, in the cubic KGdF 4 (C-KGdF 4 ), the chemical disorder of Gd 3+ /K + , increases the Gd 3+ -Gd 3+ distance and weakens the dipolar interactions, and thus leads to a large -Δ S M = 30.5 J kg −1 K −1 at 1.3 K at the magnetic field change of 10 kOe, which is more than three times of that of the commercial Gadolinium Gallium Garnet (Gd 3 Ga 5 O 12 , GGG) under the same conditions. Furthermore, the magnetic ordering temperature of 0.6 K of the C-KGdF 4 is lower than most reported Gd-based magnetocaloric materials. These excellent magnetocaloric performances suggest that C-KGdF 4 is a highly promising candidate for ultra-low-temperature magnetic refrigeration.
Nuo Duan,Hui Zhang,Yu Nie,Shijia Wu,Tingting Miao,Jie Chen,Zhouping Wang
We report a method for trace detection of bisphenol A (BPA) based on fluorescence resonance energy transfer (FRET) between lanthanide-doped KGdF4 nanoparticles (KGdF4:Tb3+ NPs) as a donor, and gold nanoparticles (AuNPs) that act as an acceptor. The KGdF4:Tb3+ NPs were modified with an aptamer recognizing BPA, and AuNPs were modified with the complementary DNA (cDNA) of the aptamer. The donor–acceptor pair was fabricated by hybridizing the aptamers and their cDNA. Thus, fluorescence of the KGdF4:Tb3+ NPs could be quenched due to the good overlap between the KGdF4:Tb3+ NP fluorescence emission and the AuNP absorption spectrum. However, on addition of BPA, the aptamers preferentially bound to BPA, forming KGdF4:Tb3+ NP–aptamer–BPA complexes. As a result, the FRET was disrupted, and the fluorescence was restored. The recovered fluorescence of the KGdF4:Tb3+ NPs was linearly proportional to the concentration of BPA in the range of 0.5 to 100 ng mL−1, with detection limits as low as 0.16 ng mL−1. The assay was applied to real samples, and the results were consistent with the results obtained using high performance liquid chromatography (HPLC) methods. We presume that this strategy can be extended to the detection of other contaminants by simply substituting the aptamer.
Hyaluronic acid (HA)-functionalized lanthanide-doped KGdF 4 nanoparticles were synthesized through two steps on a microfluidic platform. This microfluidic synthesis method allows better control of experimental conditions with lower labor and energy input than traditional beaker synthesis methods for large-scale production of nanoparticles with higher uniformity. First, Ln 3+ -doped KGdF 4 nanoparticles were ultrafast (in minutes) and continuously synthesized using a four-inlets microfluidic chip at room temperature. Then, HA is continuously functionalized on the surface of Ln 3+ -doped KGdF 4 nanoparticles using a T-shape chip through electrostatic adsorption. The synthesized nanoparticles show good uniformity, high biocompatibility, targeted cellular uptake, photoluminescence (PL) and magnetic resonance (MR) properties. This work highlights the potential of microfluidic platform for the development of multifunctional nanoparticles in biomedicine.
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